Guest Blog: Bagworms – the unknown pest

I had seen the pictures on Pinterest, with the click-bait title urging me to read more on how to “never buy mandarins again!” The little tree in the pot on the website was laden with fruit. It made me excited. By darnit – I can have my orchard in my rental, and eat from it too!

So off I went with some saved up money to procure a dwarf mandarin tree. I settled on a Miho which promised sweet, easy-to-peel, early ripening fruit particularly suited to container growing.

It went well for a while, my tree got planted in a 50l grow bucket and got watered and (seaweed) fed with the rest of my potted fruits. And truly, it sprouted masses and masses of flowers, making me believe, truly, for the first time, that the picture I found on the web might have been real fruit, not stuck-on faux globes of mandarins…

Alas, December came, and we got hit by high temperatures, and an early drought. I’m on tank water, and simply had to rein in on watering all the plants. Good for them, toughening them up a bit, I thought. But I started noticing my mandarin dropping leaves, and then dropping all those beautiful tiny little fruit that had formed from the profusion of flowers earlier in the season. I gave it some extra love and H2O, and even some specialised fertiliser, but it kept on withering away.

I attributed its decline to perhaps being particularly susceptible to hot and dry conditions, but started to really puzzle when it was only bare branches and dried twigs, while my other citrus (Meyer Lemon, Yen-Ben Lemon, Lemonade Lemon and Ugli Fruit) seemed to recover.

That’s when I spotted them.

What I had previously thought were simply remnants of stems from fruit or leaves, or bits of broken sticks on the dead branches of my tree, moved. It MOVED! A little jolt of “what the…” went through my mind, and always curious, I settled in to observe in detail this moving bit of “twig”.

Turns out that my poor mandarin was infested with bagworms. Bagworms, so says Wikipedia, are also sometimes referred to as case worms, and are species of the family Psychidae, related to Lepidoptera (moths and butterflies).

The larvae of bagworms spin a silk cocoon case, which depending on species, can range from 1cm to 15cm, as soon as it hatches, adding material from nature (twigs, seeds, leaf debris etc.) to the case as they grow, very effectively camouflaging them from predators (and me!). They then continue to feed on their host plant, with a significant infestation quickly decimating a plant. Once satiated on leaves, the male bagworm caterpillar fixes his cocoon to the host plant and pupates, emerging as a winged moth to find a mate. Female bagworms however never leave their cocoons, continually consuming leaves until they lay eggs (in their cases) and die.

In a production orchard, some types of bagworms are quite partial to Citrus plants. I can imagine that insecticidal sprays could be used to prevent them becoming a problem, but I try to run my home garden organically and spray-free as far as possible. I only had one tree with them on (trust me I had a really, really good look at all my other plants!), and dealt with my infestation by simply picking the cocoons off one by one, and dropping them in water with some bleach, trying to make sure that any eggs left by females in their cases will not be viable.

I go out every few days to see if any new ones have emerged, checking the mass of Alyssum that I under planted my Miho, and all the surrounding plants and grasses. I’ve found a few on each occasion, and will probably unfortunately miss a few, which when they hatch next season, will become a new nuisance. But at least now I know what to look out for.

As for my Miho, the main leader branch is not showing any signs of recovery, but I have four side branches that have new leaf growth. I may still be able to have my home-grown mandarins next season after all!

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2 thoughts on “Guest Blog: Bagworms – the unknown pest”

We used to grow leucadendrons for export and local markets, and the case moth was a nuisance. We did manage to control them with insecticide as it would have been next to impossible to do it by hand. There was a large population of them in our shelter- belt. They are a fascinating insect.

Thanks for your comment Kath and for sharing your experience! Here at Grow Inspired, we would only use organic to treat any pests though, and are currently treating ours with an organic oil. Have you had any luck with organic oils yourself? Claire